Leptin is produced by adipocytes, and regulates appetite by signaling levels of fat stores to the brain. Leptin is also important to reproduction. Animals without leptin receptors fail to go through puberty and those with low levels of leptin reproduce with low efficiency. Recent studies have found leptin production sites in the pituitary gland. However, little is known about mechanisms that regulate changes in leptin expression in the pituitary and there is no agreement about the cell types that express leptin. These feasibility studies are, therefore, proposed to test the overall hypothesis that gonadotrope leptin contributes to the rise in expression of pituitary leptin during the cycle, perhaps to provide a source of leptin that alters feeding in support of a pregnancy. Aim I studies will determine if gonadotropes change their expression of leptin mRNA as they are stimulated, in vivo, by GnRH and estradiol. We will use novel dual in situ hybridization protocols to learn if there are changes in gonadotropes expression of leptin that parallel those for the gonadotropin beta subunits (LHbeta and FSHbeta). Sub Aim la will focus on the periovulatory period, which is characterized by estrogen and GnRH stimulation and peak levels of gonadotropin beta subunit mRNAs. Sub Aim lb will use proestrous female rats that have mated. These studies will test leptin expression by gonadotropes during the first week of pregnancy to learn if expression changes as the reproductive system is activated. The leptin and gonadotropin mRNAs will be detected in both dispersed cells and pituitary sections. If leptin is produced in gonadotropes, it may be regulated by gonadotropin releasing hormone (GnRH) or estrogens. Aim 2 studies will learn how GnRH and/or estrogen affect expression and secretion of leptin by gonadotropes, in vitro. These studies will be conducted on freshly dispersed mixed populations of pituitary cells or enriched gonadotropes to learn if the leptin secretion seen in response to GnRH reflects that from the gonadotropes. Information from these pilot studies is vital before one can formulate and address hypotheses about the significance of leptin production in the pituitary. This information can lead to hypotheses about its impact on fertility, sexual development, or the regulation of the reproductive system. These feasibility studies will thus provide information that will allow us to design future experiments for full funding.